Semiconductor circuit elements continue to get smaller. Smaller technologies can require larger test sample sizes and lower stress, longer duration tests.
With smaller devices also come manufacturing pressures to reduce electrical contact pad sizes. Smaller contact pads can require greater probe positioning accuracy, both in XY and in Z. Probe technologies designed for smaller pads can also have a smaller margin of error in Z overtravel before they are damaged. A result may be small mechanical perturbations, which may not be a problem with relatively larger pads, e.g. 100 or 200 μm sized pads, but can cause probes to miss their pads with relatively smaller pads, e.g. 30 or 40 μm sized pads, or can even damage probes designed for smaller pads.
In U.S. Pat. No. 6,011,405, XY position of sites are determined by crossed rods. Arrays have the disadvantage of moving multiple sites with each rod. Site crosstalk makes fine adjustment a tedious, iterative process. Stiffness of the rods is an issue, both vertically and laterally. Low vertical stiffness can cause the probes to sag in the middle. Accidental application of force to the top of the array can damage probe modules. Low lateral stiffness can cause the rod to curve during adjustments from friction at the sites. Stresses built-up during alignment due to friction can relax over time with small vibrations or changes in temperature, causing drift of probe position. Mechanisms at individual sites, along with the height of two rods, limit microscope working distance. Probe card access from underneath can be cumbersome. Double-sided wedge card that probes multiple die works for one die spacing.
In U.S. Pat. No. 7,436,171, the use of individual probe sites on rails is shown, with the rail position providing gross positioning in one XY axis and with position of the site on the rail providing the other gross XY position. Each site has four fine position adjustments in X, Y, Z and about one axis. A tilting feature enables access to the probe cards for replacement from above. This design has several drawbacks. The site/rail and rail/platen interfaces rely on linear bearing trucks and rails. The trucks are elastically preloaded, which limits their stiffness. Careful matching during manufacture can improve stiffness, but can make it difficult to add trucks to the rails in the future. Additionally, position is controlled by a balance of forces that can change readily with changes in temperature of system components. Another issue with the design is access to probe cards. Tilting of the rail to change probe cards requires space. In a closely-spaced array with parallel rails, it may be necessary to move multiple rails to access one bad card on one rail. Space constraints drive the need for a relatively thin rail that can readily deflect under low loads. A soft touch may be needed to keep the rail from deflecting during site adjustments, depending on for example the span between platen guides. Additionally, the height of the fine positioning mechanism can limit microscope working distance and optical resolution.
In U.S. Pat. No. 8,402,848, versatile probe modules on positioner arms, where 3-axis positioners have bases that tilt in one or two axes. The arms cover a lot of the wafer, limiting the number of sites that can be tested simultaneously. The arms are different shapes. Over temperature changes, the arms may distort differently. Probe module planarization adjustments provided by the tilt bases are offset from the probes, which can cause large changes in Z at the probes and which can have different behavior for different arm types.